Overlay of bearers in a radio communication system

ABSTRACT

A communication system having multiple bearers overlays a relatively narrowband bearer such as P25 on a relatively wideband bearer such as LTE, for transmission of both uplink and downlink signals. The wideband bearer uses a spectrum of subcarriers which form a set of radio frequency blocks. One or more blocks or other related parts of the spectrum may be allocated to the narrowband bearer. In some cases the narrowband bearer may push through the wideband allocation using a relatively high power to dominate signals transmitted by the wideband bearer. Voice calls such as emergency calls using the narrowband bearer may be prioritized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/542,147 filed 5 Jul. 2012, which claims priority of U.S. Provisionalpatent application Ser. No. 61/504,671 filed 5 Jul. 2011, thedisclosures of which are incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

This invention relates to multi-bearer radio systems, such as systemswhich combine wideband and narrowband bearers. More particularly theinvention relates to overlay techniques involving a relatively widebandbearer such as LTE (3GPP Long Term Evolution) and one or more relativelynarrowband bearers such as P25 (APCO 25), Tetra, DMR (Digital MobileRadio), or analogue LMR (Land Mobile Radio).

BACKGROUND TO THE INVENTION

Public safety agencies around the world are considering the deploymentof broadband bearers such as LTE for improving data connectivity intheir radio systems. Utility industries such as electricity distributionare also looking to exploit similar technology. The expectation is todeploy this relatively wideband technology to operate in parallel withexisting narrow band systems such as P25. In the United States, the FCChas made specific frequency allocations supporting this model ofdeployment.

The LTE standard is based on OFDM (Orthogonal Frequency DivisionMultiplexing) of subcarriers and can be deployed in a number of channelbandwidths. A typical LTE FDD (Frequency Division Duplex) mode hasuplink/downlink pairs including bandwidths of 20 MHz, 15 MHz, 10 MHz, 5MHz, 3 MHz and 1.4 MHz. In the United States assignments of spectrumhave been made representing 10+10 MHz in 3GPP band 14 for broadbandoperation. Specifically, the US has assigned frequencies 758 MHz to 768MHz paired with 788 MHz to 798 MHz for broadband operation using LTE forPublic Safety use. In addition, an assignment has been made for PublicSafety for narrow band operation from 769 MHz to 775 MHz paired with 799to 805 MHz. In other parts of the world private broadband assignmentsare being considered for use by public safety and criticalinfrastructure.

LTE coverage is made up of a number of frequency blocks, also referredto as resource blocks. An FDD 5 MHz channel has a set 25 resource blockswhere each block is 180 kHz. Collectively the set of 25 blocks producesa bandwidth of 4.5 MHz within the 5 MHz channel with the 0.5 MHzremainder being used to contain the spectral skirts that operate withinregulated emission masks. The channel is further divided into timeslotseach of 0.5 ms, where a collection of 20 slots defines a frame. Aresource block is therefore a block extending over a period which mayinclude many timeslots. A set of frequency blocks contains many frames.

Each bearer in a wireless communication system requires a network ofbase stations to provide the channels over which users can communicate.The base stations are geographically located to provide coverage over awide area within which the users are expected to move and require voiceor data services. The users typically employ hand held or vehiclemounted terminals to communicate with the base stations. Each networkgenerally includes a scheduler or controller which determines the timingand pathway of calls through the network. Bearer networks send controlmessages which are interpreted by the user terminals, in addition tovoice and data messages which are sent between the users. In a trunkedradio system a relatively large number of users share a relatively smallnumber of frequencies, without being assigned to a fixed frequency forthe duration of each call.

SUMMARY OF THE INVENTION

It is an object of the invention to provide for improved use ofavailable frequency spectrum in a multi-bearer radio system involvingLTE and P25.

In one aspect the invention resides in a method of transmitting multipleradio bearer signals, including: providing a set of radio frequencyblocks, allocating one or more frequency blocks for transmission of oneor more signals using a first bearer, allocating one or more frequencyblocks for transmission of one or more signals using a second bearer,and transmitting the signals using their allocated frequency blocks.

Preferably the first bearer provides a relatively wideband service forwhich multiple frequency blocks are allocated, while the second bearerprovides a relatively narrowband service for which a single frequencyblock is allocated. The frequency blocks allocated to the first bearerare generally grouped together, but may be separated by one or moreblocks allocated to the second bearer. Frequency blocks allocated to thesecond bearer may lie at one end of the set of blocks. When eitherbearer ceases transmission in some or all of an allocated portion ofspectrum then the allocation available to the other bearer is generallyincreased. The signals transmitted using either bearer generally includeboth uplink signals transmitted by user terminals and downlink signalstransmitted by base stations.

In another aspect the invention resides in a method of providing radioservices using multiple bearer signals, including: providing a set ofradio frequency blocks, allocating the frequency blocks for servicesusing a first bearer, receiving a request for services using a secondbearer, and re-allocating one or more of the frequency blocks forservices using the second bearer. Signals such as voice calls andparticularly emergency calls may therefore be prioritised.

In a further aspect the invention resides in a controller for a radionetwork, having a processor and memory, the memory containinginstructions which cause the controller to carry out a method asoutlined above.

In a further aspect the invention resides in a controller for terminalunit for a radio network, having a processor and memory, the memorycontaining instructions which cause the controller to select a bearerfrom multiple available bearers for transmission and reception ofsignals as outline above.

LIST OF FIGURES

Preferred embodiments of the invention will be described with respect tothe accompanying drawings, of which:

FIGS. 1A, 1B, 1C, 1D schematically show options for frequency overlaysof P25 and LTE in a wireless communication system,

FIG. 2 shows a simple system with P25 and LTE base stations andterminals,

FIG. 3 outlines a general controller process for allocating an overlaychannel,

FIG. 4 outlines a process for prioritizing a critical call,

FIG. 5 outlines a general process for allocating a P25 channel over LTE,

FIG. 6 is a sequence diagram showing allocation of an overlay channel,

FIG. 7 outlines a scheduler process for establishing LTE overlayavailability,

FIG. 8 illustrates a terminal process for establishing overlay channels,

FIG. 9A illustrates a terminal moving through an area with multiplebearer sites,

FIG. 9B illustrates a group of terminals in an area with multiple bearersites,

FIGS. 10A, 10B, 10C show example configurations of P25 overlay on LTEspectrum,

FIGS. 11A, 11B show example configurations of LTE bandwidth expansion,

FIGS. 12A, 12B show example configurations of LTE bands split and mixedbetween P25 operation,

FIG. 13 shows a typical calculation for assessing wideband noiseperformance effects of P25 on LTE,

FIG. 14 shows an adjacent channel power analysis of P25 affecting LTE,

FIG. 15 shows an analysis of the impact of LTE emissions on P25reception,

FIG. 16 shows a co-channel analysis of the impact of LTE on P25, and

FIG. 17 shows sample measurements of co-channel analysis of the impactof LTE on P25.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings it will be appreciated the invention may beperformed in a variety of ways using LTE and P25, and possibly a rangeof other communication bearers such as the DMR or LMR. Conventionaldetails of these bearer systems need not be given in detail for askilled reader. It will also be appreciated that the embodimentsdescribed here, using FDD 5 MHz and 10 MHz, are given by way of exampleonly.

FIG. 1 shows how one or more P25 channels can operate within the samefrequency band as LTE, thus enabling efficient frequency use of theassigned spectrum. These modes are made possible through collaborationbetween LTE and P25 base stations, or collaboration between LTE and P25terminals. This collaboration can be either automatic or preconfigured.Four modes of operation are:

-   -   1A. P25 operating in a space created through reducing the        bandwidth occupancy of LTE.    -   1B. P25 operating in a push through mode using a transmission        power which is higher than relatively low powered LTE        transmissions.    -   1C. P25 operating in the skirts of LTE transmissions.    -   1D. P25 operating within a disabled resource block of LTE.

In FIG. 1A, a P25 transmission occurs in a space vacated by current LTEactivity. One example of this mode would be a contraction of LTEactivity from 5 MHz bandwidth down to another standard configurationsuch as 3 MHz or even 1.4 MHz. The converse also applies and in theabsence of P25 activity an LTE transmission can expand to occupy greaterbandwidth.

In FIG. 1B, a P25 transmission over rides current LTE activity. The P25narrow band transmission dominates the relatively low energy level usedby LTE in a particular resource block, as present at a receiving stationsuch as a base station or a terminal. This push through mode may only besuitable for emergency mode or other critical communications. It willcreate interference for LTE signals in the resource block, possibly injust one sub-channel. In practice, LTE data is spread across manyresource blocks with varying degrees of protection.

In FIG. 1C, a P25 transmission can take place in the skirts of an LTEband, or more generally, in the outer edge of an outer resource block.In this case, the P25 transmission creates little or no interference forLTE signals, as P25 signals generate minimal ACP (adjacent channelpower). Conversely, LTE creates only a low level of interference for P25signals as the power spectral density in that channel is low.

In FIG. 1D, a specific LTE resource block is either temporarily orpermanently configured for P25. In this mode, a P25 transmission havinga width of about 12.5 kHz may occur within a range of 180 kHz providedby the LTE block, and may cause low level interference with LTE, becauseLTE downlink transmissions may continue to send control information ineach timeslot. An LTE transmission may also include reference signals. Anarrow band P25 transmission may therefore interfere with one or twosub-channels. However, the signalling is spread across a relatively widefrequency so this interference is expected to be minimal.

FIG. 2 shows an example site in a radio network having an LTE basestation 20 and one or more P25 base stations 21, with a commoncontroller 27, typically a scheduler, and each with respective datastreams. The base stations may be provided together at a single site orat separated sites, and are typically locked together by a frequencyreference 22 such as GPS. The LTE and P25 parts of the network generallyhave separate schedulers or may have a joint scheduler. A unit 23 havingan LTE terminal 24 and a P25 terminal 25 are linked by a controller 26.The unit 23 can be manufactured by simply linking two existing LTE andP25 terminals using an existing device such as a laptop, or by providingan integrated dual mode device. In the case of an existing device, adedicated hub may also be provided, as an interface between a laptop andthe two terminals for example. The LTE base station 20 communicates withLTE terminal 24 according to the resources assigned to that terminal,such as full assignment or resource blocks 1 to 25 including all messagetimeslots. The P25 base station communicates with P25 terminal 25 on anassigned frequency pair which overlays the LTE spectrum, but wouldconventionally be spectrally distant from LTE transmissions. Thecontrollers 26, 27 each include a processor, memory and conventionalnetwork hardware. The memory contains software instructions which causethe respective base stations and terminals to carry out overlayprocesses as described below.

FIG. 3 shows a flow chart for a process by which controller 26 or 27 inFIG. 2 establishes a P25 connection in the presence of LTEtransmissions. The process is initially waiting for a P25 connectionrequest to be made. If a P25 connection is requested 30 then anassessment 31 is undertaken to decide if there are any LTE resourceblocks (frequency slots) available. This information is available byinterrogation the LTE scheduler which can report the availability 32 ofeither resource blocks or the current bandwidth of operation.Availability of resources may be achieved either through a change of LTEtransmission bandwidth (e.g. from 10 MHz to 5 MHz), through the use ofone or more unallocated resource blocks, or through the use of the guardband for example. If spectrum is available 33 then a P25 connection canbe established 35 according to policies of the overall system. If noresource blocks are available then push through operation may be used ifpermitted 34. If this mode is not possible then P25 access will bedenied 36.

FIG. 4 shows an approach which offers preferential allocation of P25channels in the event of the request being made for a critical voiceconnection, such as an emergency call. Although mission critical voiceis selected by way of example, the same approach can apply to othercritical information such as location data. A mission critical call isrequested 40. The current status of resource blocks is assessed 41 and asequence of decisions is made as follows. If standard P25 channels areavailable 42 then a standard P25 connection is established 43.Alternatively, if unused resource blocks (including guard bands) areavailable 44 then a P25 overlay channel is assigned 45, as opposed toestablishing a call using VOIP technology over broadband. If none of theabove options exist 46 then a P25 call may be established over anexisting allocated channel 47. Such a scenario would normally only beused for emergency calls. If all the above conditions are unsuitable,generally due to lack of P25 coverage then a VOIP call could beestablished over broadband 48.

A P25 trunked controller may have a channel list with channels which areeither standard P25 channels or overlay channels which exist somewherein an LTE bandwidth allocation. A request for a channel may be receivedon a trunked control channel. If standard P25 channels are available,such as those available within the US narrowband allocation of 769 to775 paired with 799 to 805 MHz, then the request may be assigned to astandard P25 channel. If no standard P25 channels are available oroperating according to the local system policy then an alternative is toallocate P25 channels which spectrally exist within the LTE spectrumallocation, such as portions of available spectrum within the USbroadband band allocation of 758 to 768 paired with 788 to 798 MHz. Thisassignment of frequency location can be made through interrogating adatabase of either instantaneous or preconfigured system usage.

FIG. 5 provides an example in which the standard P25 channels are allassigned. Channel assignments are maintained in a database which istypically held in the P25 controller or a joint P25/LTE systemscheduler. An LTE system with m frequency blocks that is currentlyoperating in the same area is only using 5 MHz bandwidth. The trunkedcontroller can therefore assign P25 channels in the currently unused LTEspectrum shown in this example as between frequency blocks 26 and m−1.It is preferable to avoid use of block 26 in this case but rather leavea guard band which may represent 5 frequency blocks, for example. Thetrunked controller would therefore preferentially assign P25 channels tooperate in frequency blocks 31 and above. This would reduceinterference.

The policy described so far involves assigning P25 channels to frequencylocations in which minimal interference is created. An alternativepolicy may allow the P25 channel to be assigned either within the guardband of an active LTE transmission or within a currently unused resourceblock. If block 14 in FIG. 5 currently had no user data active then aP25 channel could be assigned there at the cost of some interference,for example. Alternatively a P25 channel could be assigned at anyposition over the LTE bandwidth based upon a push through mode ofoperation, typically only in an emergency situation.

A policy of allocation within unused LTE spectrum is preferable as itcreates minimal interference issues. Operating in the skirts of the LTEtransmission is the next most favourable approach and it is estimatedthat around 300 to 400 kHz beyond the outer resource block enablesoperation with minimal interference between bearers. If neither standardP25 channel nor vacant LTE spectrum nor guard band are available thenallocation may take place on an active LTE resource block but where thisresource block is not carrying any user data. Generally, within an LTEresource block which is unused, the reference signals and controlinformation within the frame should be turned off to minimiseinterference to the P25 receiver. The use of this resource block shouldthen become restricted for the length of the P25 call. Because P25channels are 12.5 kHz wide, multiple channels could fit within the 180kHz bandwidth of an unused LTE resource block. Alternatively, a set ofresource blocks may be unused and therefore P25 channels could beestablished in more than one position.

If no resource blocks are available within a reasonable time then asecond assessment is made. If the option of P25 push through is enabledthe P25 transmission may take place anyway over the top of the LTEtransmission. This option may be enabled in the case of an emergencyconnection where connectivity via P25 overrides the importance of anydata that may be on the current resource block. These modes can beapplied for both downlink and uplink. If neither a resource block northe option of transmitting in the skirts and the push throughconfiguration is disabled then P25 access is denied.

The use of multiple possible P25 channels can be enabled through“scanning” which is a conventional technique. A P25 radio can either betuned to a fixed frequency or can be configured to scan/vote toperiodically look for activity across a range of frequencies. Ifrelevant activity is detected the radio locks onto the particularchannel reception.

Because P25 channels are 12.5 kHz wide, multiple channels can fit withinthe 180 kHz bandwidth of an unused LTE resource block. Alternatively, aset of resource blocks may be unused and therefore P25 channels could beestablished in more than one position. When resource blocks at one edgeLTE transmission are shut down this is the equivalent to changing LTEoperating between standard operating bandwidths, such as from 10 MHz to5 MHz.

FIG. 6 provides a sequence diagram relating to the example of a P25controller. A terminal asks for a connection and is allocated an LTEoverlay channel. A connection request is made to the trunked controllerwhich reviews the channel status. In this case, all standard channelsare busy but overlay channels are available. In this case because thechannels are within the LTE spectrum allocation but which are notcurrently in use. The controller now reviews current system policies.The policies are those generally used in a trunked P25 system and inthis case, it is assumed that unoccupied LTE spectrum can be used forP25, but that the skirts, guard band, push through mode and operationalresource blocks cannot be used. Some of the LTE spectrum is unused. As aresult, the P25 channel is allocated in the used LTE spectrum and thedatabase updated.

This represents an approach of dynamically expanding the missioncritical P25 operation or the broadband operations according to whichmode is required at the time. In this example we assume all standard P25channels are busy and the only channel available is the overlay channelwhich is established through interrogating a commonly accessibledatabase. The resource block available is one nominally assigned for LTEuse but which is currently inactive due to the LTE bandwidth in thatarea being 5 MHz instead of 10 MHz at that time. Hence a P25 channel isassigned to the overlay position for the duration of the call. Thedatabase is also updated so that the broadband scheduler is informed toblock access or reduce its bandwidth operation on this portion of theresource and the trunking controller is informed of success. It thensends the user to that channel.

FIG. 7 shows a complementary version of the process in FIG. 6. Here, thebroadband system, which is typically an LTE scheduler, is waiting forLTE connection requests.

Upon receiving a data connection request the scheduler may choose toallocate a user to a standard broadband position, such as portions ofavailable spectrum within the US assigned broadband band allocation of758 to 768 paired with 788 to 798 MHz. If however the P25 allocations inthat area are not being used, as established through interrogating adatabase of usage, then the broadband system may expand its bandwidth ofoperation to extend across parts of the nominal narrow band allocation,for example 769 to 775 MHz paired with 799 to 805 MHz.

An equivalent process exists on the uplink where a multi-bearer deviceis in use. A controller is illustrated as the terminal end in FIG. 2 andtypically represents a physical processor which is connected to multiplebearers. One of the main functions of this processor is to makedecisions about which bearer to use on the uplink of a multi-bearercommunication. For example, preferential selection of uplink bearers maybe made based upon availability of a bearer or upon the system policy.The policy may be to always use P25 for critical voice communicationsand only to use a broadband connection for voice if P25 is notavailable. In the system described here, the purpose of the decisionmaking process is rather to find available channels and if necessaryadopt an overlay channel approach.

FIG. 8 illustrates a terminal process for selecting which bearer to use.This process resides on the controller in FIG. 2 and interrogates boththe P25 terminal and the broadband terminal to establish currentavailability of channels, bandwidth of operation or current usage levelsof resource blocks. The information is available at a typical LTEterminal device because the device is able to detect the currentbandwidth of operation and the current allocations of uplink resource.In this particular example the table illustrates how there are many P25channels which are all in use. In this case, either guard band, unusedLTE bandwidth or even inactive resource blocks may be used forestablishing a mission critical call. If the LTE device is out of rangeof an LTE transmission then a policy may be adopted such that theterminal may or may not transmit P25 within known LTE allocations ofspectrum. This minimises the chance of interference. An alternativepolicy may require that a P25 transmission not take place if the LTEsignal strength or signal quality is above a predefined level. Thispolicy may be applied to prevent the P25 transmission located physicallyclose to an LTE receiver from causing significant interference throughwideband noise emissions. An alternative policy may be to limit thepower of the P25 transmission depending upon the LTE signal strengthbeing observed.

FIG. 9A shows a simple system where a multi-bearer unit 90 is movingthrough a geographic area which is served by multiple bearers. Basesites 91, 94 provide coverage for P25 only, on channels fn at bandwidthB 1. Base site 92 provides coverage for LTE only, on channel f3. Site 93provides both P25 and LTE. Their coverage overlaps in part but is notavailable continuously over the entire area. A network operation centre95 exercises control over the network formed by these sites and includesa scheduler. In this example, the allocation of P25 channels isnominally for critical voice activity. Initially the unit 90 can onlyconnect with site 91 using P25. Moving northeast the unit passes througha region where LTE is provided by site 93 but is only operational withina 5 MHz bandwidth. While still being served by site 91, the unitcontinues to operate on a standard P25 channel. If no standard P25channels are initially available via site 94, the unit may be allocatedto an overlay position somewhere within the currently unused 5 MHzbandwidth of the LTE coverage. A system of this kind must comply withproper RF design techniques to avoid co-channel, adjacent channel orblocking probabilities.

FIG. 9B shows another simple system where a group of radios is locatedin the same geographic area as the system in FIG. 9A. Subset A of theradios is served by base sites 91 and 93 and can communicate usingeither P25 or LTE. Subset B of the radios is served only by 91 and cancommunicate using P25. Subset C is served only by base site 93. Eachsubset could represent multiple radios or could be a single radio. Thenetwork operation centre 95 determines that subset A has access to bothP25 and LTE, that subset B only has access to P25, and that subset Conly has access to LTE. Channel resources are allocated accordingly whena group call is set up. For example, subset A may be allocated abroadband channel using LTE rather than P25 while subset B will beallocated a trunked radio channel using P25. As the radios move aroundthe geographic area resources can be re-allocated according to theavailability of channels at each site.

FIG. 10 shows spectrally an example where the LTE operation is scaleddown from one side or another to accommodate a demand for P25 channels.FIG. 10A shows the standard configuration for radio system operation inthe US with broadband LTE operational in a nominal bandwidth of 10 MHzfrom 758 to 768 MHz, and narrow band LMR operation in a block ofspectrum between 769 to 775 MHz. FIG. 10B shows an example where the LTEbandwidth reduces from a nominal 10 MHz to 5 MHz opening temporary spacefor mission critical P25 operation in the lower 5 MHz portion. FIG. 10Cshows an example where the LTE bandwidth is reduced to 3 MHz allowingtemporary P25 operation either side of LTE. It should be noted, forconvenience, here we illustrate the downlink segment of operationwhereas the apparatus described here applies equally to the uplink.

FIG. 11 shows a complementary example where P25 operation in a nominalallocation of 769 to 775 MHz is reduced. In this case, the demand forbroadband data operation exceeds the requirement for mission criticalvoice in narrow band channels. As a result, the system has extended thebroadband operation across 15 MHz and LMR operation is limited to asmall bandwidth which in this example exists between 774 and 775 MHz. Itis prudent to maintain a guard band.

FIG. 12 shows another example. In this case, broadband operation extendsacross 10 MHz but through aggregation of different positions within thespectrum range. The positioning of LMR is also split across the band toproduce an aggregate of 6 MHz for example.

An analysis of the interference effects between P25 and LTE for sampleoverlay configurations of P25 and LTE can be provided. The analysisfocuses upon the downlink. Generally there are three key forms ofinterference, co-channel (on channel), adjacent channel interference andwideband noise.

FIG. 13 shows a system example where P25 is operating with the LTEspectrum allocation but where the bandwidth of LTE operation has beenreduced such that LTE and P25 do not overlap. In this case there is noon-channel interference caused by P25 on P25 nor by LTE on P25.

FIG. 14 offers an analysis of wideband noise based on TIA performancefigures assuming the interferer is off channel. This example shows a P25transmission occurring at 50 W (47 dBm) within an 8.1 kHz bandwidth andan LTE transmission occurring with a total power of 54 dBm across thetotal occupied bandwidth of 4.5 MHz. An example transmitter power forLTE is 40 dBm but it is also typical to use a directional antenna and a14 dB gain has been selected. With reference to FIG. 14, consider theeffect of P25 transmissions on the LTE receiver. TIA 102.CAAB definesthe emission mask at 80 dBc in a 30 kHz b/w between 400 kHz and 12 MHzaway from carrier. This extends across the LTE Rx allocation. Toestimate the total energy entering the LTE Rx band, we need toaccumulate the P25 energy over the entire 4.5 MHz band. This yields afigure of 58.3 dB down from the P25 carrier power. Given this ratio, itmeans an absolute power of −11.3 dBm will be seen in the LTE terminal Rxfrom the P25 wide band emissions. This means that for a co-located LTEand P25 site the LTE terminal receiver will experience a C/I of 65.3 dB.The C/I required for a good data rate in LTE is around 19 dB hence theLTE performance will be fine and P25 will not significantly interferewith LTE. If the LTE base station and P25 base station are locatedseparately then it is possible for an LTE terminal receiver toexperience interference due to wideband noise from a P25 transmitter ifsaid transmitter is only capable of meeting the TIA definedspecification.

Considering an uplink case, given the US allocations and the standardP25 specifications, then on the uplink a P25 terminal could cause aninterference problem over the adjacent LTE uplink (just 1 MHz away) ifthe P25 terminal was close to the LTE uplink antenna and the LTEterminal were far away. The LTE terminal will be operating power controlanyway and its modulation and coding rate changes according to theobserved interference level.

Referring to FIG. 14, we can estimate the ACPR case. TIA 102-CAAB-Bsection 3.2.8.2 defines the adjacent channel power ratio of the P25transmission. Notably it defines the power ratio 37.5 kHz off frequencyas 60 dB in a 25 kHz bandwidth. It is therefore possible to estimate howclose a P25 transmission can operate to the edge of an LTE emission.Assuming interference from the P25 emission applies across the whole ofthe nearest resource block of 180 kHz. Given this, the 60 dB figurewithin 25 kHz becomes 51.4 dB across the 180 kHz bandwidth. In theexample shown, we assume a 47 dBm P25 transmission and a total of LTEtransmission power of 54 dBm (including the gain of a 14 dB directionantenna). Based on this LTE transmission power, we can estimate thepower within the single resource block on the edge as being 40 dBm (i.e.54 dB−10*log 10(1/25). Given this configuration, the C/I ratio withinthe resource block at the edge is approximately 44.4 dB. This suggeststhat P25 could operate safely at a position closer to LTE than the 1 MHzguard band currently specified. Once again however, if base stations arenot co-located then a wider frequency separation would be required.

FIG. 15 analyses the case where LTE transmission may interfere with P25reception. We simply use one of the 3GPP base station masks as anexample. This mask is applied to the scenario with an antenna gain of 14dB and shown in blue. The specification assumes a 100 kHz b/w. Theenergy arriving in a 8.1 kHz bandwidth must be corrected. Assuming thepath loss of over the P25 channel and the LTE channel are the same andthe terminal is not so far away as to be below the P25 sensitivity limitthen the C/I seen at the P25 receiver will be 61 dB. The C/I requiredfor >=2% BER is typically 16 dB hence LTE will not significantly affectthe performance of a P25 receiver.

FIG. 1B shows an example where P25 operation occurs directly over thetop of an LTE transmission. Here, we examine the impact on the P25reception (assume a receiver noise B/w of 8.1 khz) through examining theexpected co-channel performance levels.

FIG. 16 illustrates a co-channel example where X represents a wanted P25signal at the edge of range where for example this may be −118 dBm for a1% BER for an example radio. Typical specifications suggest that thereceiver of the wanted P25 signal should be capable of maintaining thesame level of BER when another P25 signal operating on the samefrequency which is 9 dB weaker than the wanted. Specifically this istypically tested by increasing the wanted signal level by 3 dB, thenstarting from a substantially lower power P25 interferer (with apredefined transmission pattern) and gradually increasing the interferepower until such time the BER observed at the wanted received returns toa nominal value.

In this case we have chosen a nominal value of 1% which typicallyrepresents a very good voice signal. Now we consider the effect of anLTE transmission occurring over 4.5 MHz in a channel allocation of 5MHz. Also assume the transmission is fully occupied with data (worstpossible case). LTE is now an interferer over P25.

The energy from an LTE transmission spilling into the narrow band of atypical P25 receiver would be approximately 27.4 dB (10*log10(8100/45e5) down compared to the total power of an LTE transmission.Given this and working with a co-channel requirement of 9 dB, we canestimate that an LTE transmission occurring over a P25 transmissioncould be 18.4 dB more powerful than P25 before causing a co-channelproblem larger than P25. This means that for a co-located P25 and LTEsite, as long as the P25 source is always more than 18.4 dB morepowerful that LTE within the P25 bandwidth then P25 shall not observe aBER worse than 1% due to LTE interference.

Practically one would want a larger protection margin. FIG. 14 showsreal measurements undertaken using the above configuration whereupon theco-channel performance observed was approximately 18 dB. In this test,the LTE interfere was incrementally moved off channel hence we see theimproving level of performance as we traverse the skirts of the LTEtransmission.

FIG. 1C illustrated the option of operating P25 in the skirts (or guardband) adjacent to an LTE transmission. Referring again to FIG. 16, theskirts of the LTE transmission are naturally lower power than the mainbandwidth. The co-channel performance was about 18 dB. Moving offfrequency shows the impact of the transmission skirts. In thisparticular case there is a rapid increase in the co-channel performancereaching as much as 50 dB. In other words, subject to the system designP25 could operate in the skirts of the P25 transmission as long as aguard band of at least (approx) 300 kHz is maintained though this mayincrease depending upon system design.

Consider the case of a P25 transmission at 47 dBm and an LTEtransmission at 40 dBm. In this case the C/I seen at the P25 terminal upto 2 MHz offset from the LTE centre frequency would be approximate47−12.6−14=20.4 dB which is close to the observed co-channel performanceshown in FIG. 17. The C/I seen at the P25 terminal at 2.3 MHz off wouldapproximate to 47−12.6+17−14=37.4 dB. The 17 dB improvement is derivedfrom FIG. 16 which suggests that as long as the station operates>300 kHzoff the wanted channel then P25 receiver performance is acceptable. TheC/I improves beyond this point.

FIG. 1D illustrated the option of operating P25 within an unusedresource block within LTE. Consider the case where a P25 transmission isoperating over an active LTE transmission i.e. push through. This modeof operation is not recommended but it is worth analysing. A typicaltransmission powers: a) The P25 transmission at 50 W (47 dBm) and thisoccurs with a bandwidth of 8.1 kHz. b) The LTE transmission is 10 W (40dBm) and this occurs in a bandwidth of 4.5 MHz. The +40 dBm LTEtransmission will offer just 40 dBm-27.4 dBm into the wanted P25channel. i.e. +12.6 dBm. This means the C/I interference ratio seen atthe P25 receiver is 47−12.6 dB=+34.4 dB. If we add an assumption of a 14dB directional antenna then this means the C/I ratio seen at the P25receiver is 47−12.6−14=20.4 dB. This figure is only just acceptable forgood operation.

An individual LTE user can be allocated transmission resources withinone or more resource blocks, time slotted within each resource block.Through disabling one or more RB within the LTE transmission allows thepossibility of deploying P25 in this unused space. Measurements of asample LTE system on the downlink in which one LTE resource block is noallocated to a user suggests that an unused resource block may be 10 dBdown in is power compared to an fully used resource block. One mightexpect the power drop to be more substantial but it is important toremember that even in unused resource blocks, signalling and referencesignals can still be present. The reference signals and control signalsideally need to be shut down to provide best performance on the P25downlink. This means that P25 operating in an unused resource blockwould observe approximately a 30.4 dB C/I which is a good performancefigure.

The invention claimed is:
 1. A method of data communication, comprising:receiving data associated with a radio moving on a path, wherein a firstpart of the path of the radio is located within a first region and asecond part of the path of the radio is located within a second region;determining, at a network operation centre, that the first part of thepath of the radio has access to resources assigned to a trunked radiosystem; determining that the second part of the path of the radio hasaccess to resources assigned to the trunked radio system and resourcesassigned to a broadband data system; and allocating resources in thefirst region using resources assigned to the trunked radio system and inthe second region using resources assigned to the broadband data system,and providing data to the radio on the first part of the path by thetrunked radio system resources and not the broadband data systemresources and on the second part of the path by the broadband datasystem resources and not the trunked radio system resources.
 2. A methodaccording to claim 1 further comprising: receiving data associated withthe radio moving on a third part of the path located within a thirdregion; determining that the third part of the path of the radio hasaccess to resources assigned to the broadband data system and not thetrunked radio system; allocating resources in the third region usingresources assigned to the broadband data system; and providing data tothe radio on the third part of the path by the broadband data system. 3.A method according to claim 1 wherein the resources assigned to thetrunked radio system include frequencies 769-775 MHz and 799-805 MHz. 4.A method according to claim 1 wherein the resources assigned to thebroadband data system include frequencies 758-768 MHz and 788-798 MHz.5. A method according to claim 1 wherein the resources allocated in thefirst region are used for a trunked radio channel.
 6. A method accordingto claim 1 wherein the resources allocated in the second region are usedfor a trunked radio channel.
 7. A method according to claim 1 whereinthe resources allocated in the second region are used for a broadbanddata channel.
 8. A data communication system comprising: a trunked radiosystem and a broadband data system, a network operation centre coupledto the trunked radio system and the broadband data system, the networkoperation centre including a processor and a memory, the memoryincluding software instructions which are used by the processor for:receiving data associated with a radio moving on a path, wherein a firstpart of the path of the radio is located within a first region and asecond part of the path of the radio is located within a second region;determining that the first part of the path of the radio has access toresources assigned to a trunked radio system; determining that thesecond part of the path of the radio has access to resources assigned tothe trunked radio system and resources assigned to a broadband datasystem; and allocating resources in the first region using resourcesassigned to the trunked radio system and in the second region usingresources assigned to the broadband data system, and providing the datato the radio on the first part of the path by the trunked radio systemresources and not the broadband data system resources and on the secondpart of the path by the broadband data system resources and not thetrunked radio system resources.
 9. A method according to claim 8 whereinthe resources allocated in the first region are used for a trunked radiochannel.
 10. A method according to claim 1 wherein the resourcesallocated in the second region are used for a trunked radio channel. 11.A method according to claim 1 wherein the resources allocated in thesecond region are used for a broadband data channel.
 12. A method ofdata communication, comprising: receiving data associated with a groupof radios, wherein a first subset of the group of radios is locatedwithin a first region and a second subset of the group of radios islocated within a second region; determining, at a network operationcentre, that the first subset of radios has access to resources assignedto a broadband data system and resources assigned to a trunked radiosystem; determining that radios included in the second subset of radiosdo not have access to resources assigned to the broadband data system;and allocating resources in the first region using resources assigned tothe broadband data system and in the second region using resourcesassigned to the trunked radio system, and subsequently providing data tothe first subset of radios by the broadband data system resources andnot the trunked radio system resources and to the second subset ofradios by the trunked radio system resources and not the broadband datasystem resources.
 13. A method according to claim 12 wherein a thirdsubset of the radios is located within a third region, furthercomprising: determining that radios included in the third subset ofradios do not have access to resources assigned to the trunked radiosystem; allocating resources in the third region using resourcesassigned to the broadband data system; and providing data to the thirdsubset of radios by the broadband data system and not the trunked radiosystem.
 14. A method according to claim 13 wherein the resourcesassigned to the trunked radio system include frequencies 769-775 MHz and799-805 MHz.
 15. A method according to claim 13 wherein the resourcesassigned to the broadband data system include frequencies 758-768 MHzand 788-798 MHz.
 16. A method according to claim 13 wherein theresources allocated in the first region are used for a trunked radiochannel.
 17. A method according to claim 13 wherein the resourcesallocated in the second region are used for a trunked radio channel. 18.A method according to claim 13 wherein the resources allocated in thesecond region are used for a broadband data channel.
 19. A datacommunication system comprising: a trunked radio system and a broadbanddata system, a network operation centre coupled to the trunked radiosystem and the broadband data system, the network operation centreincluding a processor and a memory, the memory including softwareinstructions which are used by the processor for: receiving dataassociated with a group of radios, wherein a first subset of the groupof radios is located within a first region and a second subset of thegroup of radios is located within a second region; determining that thefirst subset of radios has access to resources assigned to a broadbanddata system and resources assigned to a trunked radio system;determining that radios included in the second subset of radios do nothave access to resources assigned to the broadband data system; andallocating resources in the first region using resources assigned to thebroadband data system and in the second region using resources assignedto the trunked radio system, and subsequently providing data to thefirst subset of radios by the broadband data system resources and notthe trunked radio system resources and to the second subset of radios bythe trunked radio system resources and not the broadband data systemresources.
 20. A method according to claim 19 wherein the resourcesallocated in the first region are used for a trunked radio channel. 21.A method according to claim 19 wherein the resources allocated in thesecond region are used for a trunked radio channel.
 22. A methodaccording to claim 19 wherein the resources allocated in the secondregion are used for a broadband data channel.